1. Field of the Invention
The present invention relates to a combined MR (Magnetoresistance)/Inductive thin film magnetic head mounted on, e.g., a hard disk drive and, more particularly, to a thin film magnetic head in which reproducing characteristics are improved by putting the magnetization of a shield layer into a single domain state.
2. Description of the Related Art
FIG. 8 is an enlarged sectional view showing a conventional thin film magnetic head viewed from the side opposing a recording medium.
This thin film magnetic head has the following arrangement. That is, a read head h1 using a magnetoresistance effect and a write inductive head h2 are stacked on the end face on a trailing side of a slider which constitutes, e.g., a floating type head.
A lower shield layer 1 serving as the lowest layer of the thin film magnetic head shown in FIG. 8 consists of a soft magnetic material such as Sendust or an Ni--Fe alloy (permalloy). The Sendust is generally known as a soft isotropic magnetic material, and the permalloy is generally known as a soft magnetic material having uniaxial anisotropy.
A lower gap layer 2 consisting of a non-magnetic material such as an Al.sub.2 O.sub.3 (aluminum oxide) is formed on the upper surface of the lower shield layer 1. A magnetoresistance element layer 3 is formed on the upper surface of the lower gap layer 2. The magnetoresistance element layer 3 is constituted by three layers which are a soft magnetic layer (SAL layer: soft adjacent layer), a non-magnetic layer (SHUNT layer), and a magnetoresistance layer (MR layer) sequentially laminated from the bottom. In general, the magnetoresistance layer is an Ni--Fe alloy (permalloy) layer, and the non-magnetic layer is a Ta (tantalum) layer. The soft magnetic layer consists of an Ni--Fe--Nb alloy.
Hard bias layers 4 are formed as longitudinal bias layers on both the sides of the magnetoresistance element layer 3. A longitudinal bias magnetic field in the hard bias layer 4 is oriented in an X direction, and the MR layer of the magnetoresistance element layer 3 is oriented in the X direction in FIG. 8, so that a single magnetic domain state can be obtained.
A main lead layer 5 consisting of a non-magnetic material such as Cu (copper) or W (tungsten) having a low electric resistance is formed on the upper surface of the hard bias layer 4. An upper gap layer 6 consisting of a non-magnetic material such as alumina is formed on the upper surface of the main lead layer 5.
An upper shield layer (lower core layer) 7 is formed on the upper surface of the upper gap layer 6 by plating a permalloy or the like. The upper shield layer 7 has a core function on the reading side of the inductive head h2 and an upper shield function for the read head h1. On the read head h1, a gap length Gl1 is determined by an interval between the lower shield layer 1 and the upper shield layer 7.
A gap layer (non-magnetic material layer) 8 consisting of alumina or the like and an insulating layer (not shown) consisting of polyimide or a resist material are laminated on the upper surface of the upper shield layer 7, and a coil layer 9 which is patterned to have a spiral shape is formed on the upper surface of the insulating layer. The coil layer 9 consists of a non-magnetic electrically conductive material such as Cu (copper) having a low electric resistance. The coil layer 9 is surrounded by an insulating layer (not shown) consisting of polyimide or a resist material, and an upper core layer 10 consisting of a magnetic material such as a permalloy is formed on the upper surface of the insulating layer by plating. The upper core layer 10 functions as a core portion on the trailing side of the inductive head h2 for giving a recording magnetic field to a recording medium.
The upper core layer 10 opposes a magnetic gap through the gap layer 8 on the upper shield layer 7 on the side opposing the recording medium as shown in FIG. 8. The magnetic gap has a magnetic gap length Gl2 and gives a recording magnetic field to a recording medium. A protective layer 11 consisting of alumina is arranged on the upper core layer 10.
On the read head h1, the MR layer of the magnetoresistance element layer 3 has a resistance which is changed by the external magnetic field (direction perpendicular to the drawing paper surface). On the read head h1, signals of the recording medium are read by using the change in resistance.
The shield layers 1 and 7 are formed on the upper and lower surfaces of the MR layer, and Barkhousen noise caused by the changes of irregular magnetic domains of the shield layers 1 and 7 is transmitted to the MR layer by an mutual effect and adversely affects an output signal from the MR layer.
In order to improve the reliability of the output signal from the MR layer, external noise flowing into the MR layer of the magnetoresistance element layer 3 must be reduced. For this purpose, the following scheme is considered. That is, the magnetization directions of the lower shield layer 1 and the upper shield layer 7 are oriented in an easy axis (X direction) of magnetization, thereby putting into the lower and the upper shield layers 1 and 7 into a single magnetic domain state, and the magnetization inversion (magnetic reversibility) of the shield layers 1 and 7 must be made preferable.
As a method of controlling the magnetization directions of the shield layers 1 and 7, the following method is conventionally used. That is, when the lower shield layer 1 and the upper shield layer 7 consist of a soft magnetic material which can give uniaxial anisotropy like a permalloy or a Co (cobalt)-based amorphous alloy, film formation and an annealing process are performed in a magnetic field such that the easy axes of the lower shield layer 1 and the upper shield layer 7 are oriented in the X direction shown in FIG. 8, or magnetization is performed such that the X direction becomes the easy axis of magnetization after the film formation and the annealing process.
However, even if film formation and an annealing process are performed in a magnetic field, the magnetization directions of the lower shield layer 1 and the upper shield layer 7 are not completely oriented in the easy axis of magnetization (X direction). More specifically, in the lower shield layer 1 and the upper shield layer 7, there are some groups of magnetic moments which are inclined in a directions slightly shifted from the average easy axis of magnetization. That is, a state wherein magnetic anisotropy is dispersed (anisotropic dispersion) is macroscopically accomplished.
When anisotropic dispersion occurs in the lower shield layer 1 and the upper shield layer 7, the hysteresis of the thin film magnetic head expands as a whole to increase a coercive force. For this reason, not only the magnetic reversibilities of the shield layers 1 and 7 in a hard axis of magnetization (vertical direction in FIG. 8) are degraded, but also Barkhousen noise transmitted to the MR layer of the magnetoresistance element layer 3 which can obtain a magnetoresistance effect increases. As a result, the reliability of an output signal is considerably degraded with respect to reproducing characteristics in, especially, a high-frequency region.
When the magnetic reversibilities of the shield layers 1 and 7 are degraded, the following problem also arises. That is, a shield function inherent in a shield layer such as a function of shielding the MR layer of the magnetoresistance element layer 3 from recording noise of a recording medium is degraded.
FIG. 9 shows a prior art obtained by improving the structure of the read head h1 of the thin film magnetic head shown in FIG. 8. FIG. 9 is a partially enlarged sectional view showing the thin film magnetic head viewed from the side opposing a magnetic medium.
As shown in FIG. 9, an antiferromagnetic layer 20 consisting of, e.g., an Ni--Mn (nickel-manganese) alloy on the entire surface of the lower shield layer 1 consisting of a soft magnetic material such as Co (cobalt) or a permalloy. When the lower shield layer 1 and the antiferromagnetic layer 20 are formed to be adjacent to each other, the magnetization of the lower shield layer 1 is put into a single domain state and pinned such that the X direction in FIG. 9 is oriented in an easy axis of magnetization by an exchange anisotropic magnetic field caused by exchange coupling on the boundary surface between the lower shield layer 1 and the antiferromagnetic layer 20.
Similarly, an antiferromagnetic layer 21 is also formed on the lower surface of the upper shield layer 7, and the magnetization of the upper shield layer 7 is put into a single domain state and pinned such that the X direction in FIG. 9 is oriented in an easy axis of magnetization by an exchange anisotropic magnetic field between the upper shield layer 7 and the antiferromagnetic layer 21.
When the magnetization of the lower shield layer 1 and the upper shield layer 7 is put into a single domain state and pinned such that the X direction in FIG. 9 is oriented in the easy axis of magnetization by the exchange anisotropic magnetic fields between the lower shield layer 1 and the antiferromagnetic layer 20 and between the upper shield layer 7 and the antiferromagnetic layer 21, no anisotropic dispersion occurs in the lower shield layer 1 or 7. Therefore, a coercive force in the hard axis of magnetization (direction perpendicular to the drawing paper surface) of the entire thin film magnetic head decreases, so that the magnetic reversibilities of the shield layers 1 and 7 may be improved. As a result, an output from the MR layer of the magnetoresistance element layer 3 is free from Barkhousen nose.
However, in the structure shown in FIG. 9, the lower shield layer 1 and the upper shield layer 7 are put into a single domain state and pinned such that the X direction in FIG. 9 is oriented in the easy axis of magnetization by the exchange anisotropic magnetic fields between the lower shield layer 1 and the antiferromagnetic layer 20 and between the upper shield layer 7 and the antiferromagnetic layer 21. For this reason, the soft magnetic characteristics in the hard axis of magnetization (direction perpendicular to the drawing paper surface) in the lower shield layer 1 and the upper shield layer 7 are degraded, and magnetic permeabilities in the hard axes of magnetization of the shield layers 1 and 7 are degraded. The shield functions of the shield layers 1 and 7 are degraded because of degradation of the magnetic permeabilities. Therefore, the MR layer easily leads recording noise to degrade the reproducing characteristics.
In order to increase the resolution of a leakage magnetic field from a recording medium, the gap length Gl1 determined by the interval between the lower shield layer 1 and the upper shield layer 7 is preferably small. For this purpose, the lower gap layer 2 and the upper gap layer 6 are preferably formed to have as smaller thicknesses as possible. However, in the structure shown in FIG. 9, the antiferromagnetic layer 20 is formed on the upper surface of the lower shield layer 1, and the antiferromagnetic layer 21 is formed on the lower surface of the upper shield layer 7. For this reason, the gap length Gl1 is increased by the thicknesses of the antiferromagnetic layers 20 and 21, and a problem that a narrow gap cannot be designed arises.